Convergent synthesis of the methyl glycosides of a tetra- and a pentasaccharide fragment of the Shigella flexneri serotype 2a O-specific polysaccharide

Article abstract of DOI:10.1016/S0957-4166(02)00580-3

The branched pentasaccharide, α-L-Rhap-(1→3)-[α-D-Glcp-(1→4)]-α-L-Rhap- (1→3)-β-D-GlcNAcp-(1→2)-α-L-Rhap (B(E)CDA) and the corresponding linear tetrasaccharide (ECDA), which are part of the Shigella flexneri serotype 2a O-antigen, were synthesized as thei

Full text of DOI:10.1016/S0957-4166(02)00580-3

TETRAHEDRON:
ASYMMETRY
Pergamon
Tetrahedron: Asymmetry 13 (2002) 2211–2222
Convergent synthesis of the methyl glycosides of a tetra- and a
pentasaccharide fragment of the Shigella flexneri serotype 2a
O-specific polysaccharide†
Fabienne Segat-Dioury‡ and Laurence A. Mulard*
Unite´ de Chimie Organique, URA CNRS 2128, Institut Pasteur, 28 rue du Dr. Roux, 75724 Paris Cedex 15, France
Received 24 July 2002; accepted 23 September 2002
Abstract—The branched pentasaccharide, a-
L
-Rhap-(1“3)-[a-
D
-Glcp-(1“4)]-a-
L
-Rhap-(1“3)-b-
D
-GlcNAcp-(1“2)-a-L-Rhap
(B(E)CDA) and the corresponding linear tetrasaccharide (ECDA), which are part of the Shigella flexneri serotype 2a O-antigen,
were synthesized as their methyl glycosides according to a convergent strategy. The syntheses rely on the use of suitable B(E)C
and EC trichloroacetimidate donors, respectively, and involve an appropriate DA acceptor which bears an isopropylidene acetal
to block OH-4 and OH-6 of residue D. The preparation of the related linear CDA-OMe trisaccharide, which was used as a model,
is also described. © 2002 Elsevier Science Ltd. All rights reserved.
and immunogenicity in humans of detoxified LPS con-
jugated to protein carriers were demonstrated for sev-
eral bacterial strains,6 including Shigella flexneri 2a.7
There is evidence that conjugates incorporating carbo-
hydrate structures shorter than the native bacterial
polysaccharide may be immunogenic as well.8 Indeed,
haptens mimicking the average conformation of ‘pro-
tective’ epitopes may be the minimal structures required
for the corresponding conjugates to induce homologous
protective antibodies.
1. Introduction
Shigella flexneri serotype 2a, a Gram negative bac-
terium which is pathogenic in humans only, is the
major causative agent of the endemic form of shigellosis
or bacillary dysentery.2 To date there is no licensed
vaccine against this pathogen, which is resistant to the
first line of available antibiotics in several countries.2
As for other non-capsulated Gram negative bacteria, it
is believed that the O-specific polysaccharide moiety
(O-SP) of its surface lipopolysaccharide (LPS) serves as
a protective antigen and that serum antibodies directed
to it may provide protection against homologous infec-
tions.3 That carbohydrates could be used as vaccines to
elicit type-specific protection has been demonstrated
previously.4 At present, vaccination with purified cap-
sular polysaccharides (CPs) protects adults and older
children from infections such as those caused by Strep-
tococcus pneumoniae, Neisseria meningitidis or
Salmonella typhi.5 Bacterial O-SPs are much shorter
than CPs and often behave as haptens. They are not
immunogenic in humans as such. However, the safety
As part of an ongoing project aimed at characterizing
the carbohydrate epitopes recognized by a set of mono-
clonal antibodies protective against S. flexneri 2a infec-
tion,9 the molecular interaction between S. flexneri 2a
O-SP and such antibodies is under investigation in the
laboratory. Our approach is based on the use of syn-
thetic oligosaccharides representative of the native O-
SP. The latter is a regular heteropolysaccharide whose
biological repeating unit is the branched pentasaccha-
ride I, composed of a-
L
-rhamnoses, 2-acetamido-2-
deoxy-b- -glucose, and a branched a-
D
D
-glucose.10,11
* Corresponding author. Tel.: (+33) 1-40-61-36-77; fax: (+33) 1-45-68-84-04; e-mail: lmulard@pasteur.fr
†
Part 8 of the series ‘Synthesis of ligands related to the O-specific polysaccharides of Shigella flexneri serotype 2a and S. flexneri serotype 5a’.
For part 7, see: Ref. 1.
‡ Present address: Laboratoire de Chimie Organique, URA CNRS 7084, CNAM, 292 Rue St-Martin, 75141 Paris Cedex 03, France.
0957-4166/02/$ - see front matter © 2002 Elsevier Science Ltd. All rights reserved.
PII: S0957-4166(02)00580-3

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F. Segat-Dioury, L. A. Mulard / Tetrahedron: Asymmetry 13 (2002) 2211–2222
The preparation of the required frame-shifted di-, tri-,
tetra- and pentasaccharides, all bearing the characteris-
tic EC ramification, was undertaken.12,13 Herein, we
describe the convergent syntheses of the linear tetra-
saccharide ECDA and the branched pentasaccharide
B(E)CDA. The target compounds were synthesized as
their methyl glycosides 1 and 2, respectively, with the
natural a-anomeric configuration at their reducing end
terminus to allow both conformational analysis and
binding studies in solution. The known linear trisaccha-
ride 3,14 common to all S. flexneri O-antigens was
synthesized as a model compound.
2.1. Synthesis of the linear trisaccharide CDA-OMe, 3
(Scheme 2)
Considering the structure of the targets, we reasoned
that the synthesis of the known trisaccharide 3 could
help as a model in the design of the blockwise strategy
to 1 and 2. For this reason, the preparation of 12 was
studied rather closely. Indeed, when performed in the
presence of a catalytic amount of trimethylsilyl tri-
fluoromethanesulfonate (TMSOTf), the condensation
of the disaccharide acceptor 4 and donor23 11 resulted
in a mixture from which the target 12 (28%) and a
trisaccharide contaminant (13%) were isolated in a 2:1
ratio. Based on mass spectrometry and NMR data, the
latter was assumed to be the bC-anomer 13. The use of
boron trifluoride etherate complex (BF3·OEt2), known
to be a milder glycosylation promoter, was more satis-
factory: The yield of the targeted aC-anomer 12 was
80% and that of the contaminant bC-anomer 13 was
8%. Deprotection of 12 involved aqueous trifluoro-
acetic acid (TFA) mediated hydrolysis of the isoprop-
ylidene group to give the diol 14 (95%), subsequent
Zemple´n deacetylation into the intermediate 15 (98%),
and final hydrogenolysis to give the targeted CDA-
OMe trisaccharide 3 (82%).
2. Results and discussion
The syntheses of the targets 1 and 2 follow a common
disconnection approach (Scheme 1) involving the
known DA acceptor15 4 and two distinct donors having
a participating group at position 2 of residue C, namely
the trichloroacetimidate12 5 and the trisaccharide 6,
respectively. The efficacy of such a disconnection
approach involving donors possessing at their reducing
end a rhamnopyranose residue non-glycosylated at
position 2, was demonstrated earlier in the synthesis of
linear penta- and heptasaccharide fragments of the S.
flexneri Y O-SP, which features the tetrasaccharide
ABCD as its repeating unit.16 Additionally, in order to
prevent any extensive loss of material during the final
deprotection steps, we reasoned that the use of a DA
acceptor involving a D residue bearing an unmasked
N-acetamido function was advantageous.15 Such a
strategy may also prevent unsatisfactory glycosylation
yields as was reported earlier in closely related situa-
tions.17 In the present case, the overall synthesis is
based on the use of the trichloroacetimidate (TCA)
chemistry.18 Indeed, the key EC disaccharide12 7, which
was used as a common intermediate for the preparation
of both trichloroacetimidates 5 and 6, derived from the
condensation of the perbenzylated glucopyranosyl
donor19,20 9 with a suitable rhamnopyranosyl acceptor21
10 bearing orthogonal protecting groups. Moreover, in
the case of the branched pentasaccharide 2, the
rhamnopyranosyl donor22 8, eventually allowing fur-
ther extension at position 2, was chosen as a readily
available precursor to residue B.
2.2. Synthesis of the linear tetrasaccharide ECDA-
OMe, 1 (Scheme 3)
The fully protected disaccharide 18 is a key intermedi-
ate in the preparation of both 1 and 2. In preceding
reports, it was synthesized according to two methodolo-
gies involving either the trichloroacetate donor24 16 or
the fluoride donor12 17 (Fig. 1). Both approaches
yielded the required a-anomer 18 in yields close to 55%.
Further investigation of this compound showed that
under appropriate conditions based on the use of a
catalytic amount of TMSOTf, condensation of the
trichloroacetimidate donor 9 with the rhamnopyran-
oside acceptor 10 gave the target 18 in over 70%
isolated yield. Nevertheless, the b-anomer 19 was also
formed, indeed the estimated a/b ratio was approxi-
mately 4/1. This latter approach, involving the inverted
procedure25,26 in order to prevent extensive degradation

F. Segat-Dioury, L. A. Mulard / Tetrahedron: Asymmetry 13 (2002) 2211–2222
2213
Scheme 1. Retrosynthetic approach to the targets 1 and 2.
and 27% yield when CH2Cl2 and Et2O were used as the
solvent, respectively. In the latter case, a side-product
to which structure 21 was tentatively assigned based on
mass spectrometry analysis and experience gained in
the CDA-OMe series, was also isolated (7%). As
already observed in the preparation of the related
trisaccharide 3, the use of BF3·OEt2 as the Lewis acid in
the glycosylation process proved to be more satisfac-
tory. Indeed, when run in Et2O, the glycosidation of 4
and 5 proceeded with exclusive a-stereochemistry to
give 20 in 88% yield. The stereochemistry of the link-
Figure 1.
of the reactive donor 9, was thus definitely adopted. As
described previously,12 acidic hydrolysis of the iso-
propylidene acetal 18 gave the diol 7, which was next
benzoylated, deallylated and subsequently activated
into the known trichloroacetimidate disaccharide 5.
When performed in the presence of a catalytic amount
of TMSOTf, the condensation of precursors 4 and 5
was rather slow and did not go to completion. The fully
protected tetrasaccharide 20 was, at best, isolated in 10
1
ages in 20 was ascertained based on the JC,H hetero-
nuclear coupling constants,27,28 which were 164, 171,
167, and 172 Hz for carbons 1D, 1A, 1E, and 1C,
respectively. Complete deprotection of 20 was per-
formed as described for the preparation of 3, to afford
sequentially the partially deblocked diol 22 (92%), the
debenzoylated 23 (98%), and finally the targeted
ECDA-OMe tetrasaccharide 1 (85%).

2214
F. Segat-Dioury, L. A. Mulard / Tetrahedron: Asymmetry 13 (2002) 2211–2222
Scheme 2. Reagents and conditions: (a) BF3·OEt2, Et2O, −78“0°C (80%); (b) TMSOTf, Et2O, −78“0°C (28%); (c) 50% aq. TFA,
CH2Cl2, 0°C (95%); (d) MeONa cat., MeOH/CH2Cl2, rt (98%); (e) H2, Pd/C, MeOH/AcOH, rt (82%).
Scheme 3. Reagents and conditions: (a) TMSOTf, Et2O, −78“−55°C (73%); (b)–(e) see Ref. 12; (f) BF3·OEt2, Et2O (88%); (g) 50%
aq. TFA, CH2Cl2, 0°C (92%); (h) MeONa cat., MeOH/CH2Cl2 (98%); (i) H2, Pd/C, MeOH/AcOH (85%).
tecting group in disaccharide 18 (Scheme 3), was
regioselectively benzoylated at position 2C according to
2.3. Synthesis of the branched pentasaccharide
B(E)CDA-OMe, 2 (Scheme 4)
a
two-step procedure involving (i) reaction with
The encouraging results obtained in the condensation
of the disaccharide donor 5 and acceptor 4 prompted
the investigation of the use of the trisaccharide donor 6
in the synthesis of 2. Thus, the crude diol 7, resulting
from the selective hydrolysis of the isopropylidene pro-
trimethyl orthobenzoate in the presence of a catalytic
amount of camphorsulfonic acid (CSA), and (ii)
regioselective opening of the resulting orthoester using
50% aq. TFA, to give 24 in 87% yield from the key
intermediate 18. Condensation of the appropriately

F. Segat-Dioury, L. A. Mulard / Tetrahedron: Asymmetry 13 (2002) 2211–2222
2215
3. Conclusion
functionalized acceptor 24 with the trichloroacetimidate
donor 8, which was readily available by standard pro-
tecting group/activation strategies,22 was performed in
Et2O, in the presence of a catalytic amount of
TMSOTf, to afford the a-linked trisaccharide 25 (97%).
The fully protected 25 was de-O-allylated into the
hemiacetal 26 (75%) using PdCl2 in acetic acid.29 The
selected trichloroacetimidate anomeric leaving group
was introduced by treatment of 26 with trichloroace-
tonitrile in the presence of DBU, which resulted in the
formation of 6 (83%). Several signals in the correspond-
ing 13C NMR spectrum were highly distorted, or even
absent as in the case of C-3C and C-4C, indicating that
the donor 6 was most probably sterically hindered.
Nevertheless, BF3·OEt2-mediated glycosylation of
donor 6 with acceptor 4 resulted in the isolation of the
fully protected pentasaccharide 27 in high yield (81%).
Deacylation of the latter to give 28 (90%) was per-
formed under Zemple´n conditions. However, debenzoyl-
ation at position 2C of 27 was slow and required
heating in order to be completed satisfactorily. Similar
behaviour was observed previously in related series,1
and most probably derived from steric hindrance in 27.
Indeed, other authors have pointed out that the classi-
cal Zemple´n procedure failed to remove hindered or
isolated O-acetyl groups.30 More conveniently, acidic
hydrolysis of 27 allowing the selective removal of the
isopropylidene group and subsequent transesterification
gave 29 (82%) which was finally converted to the target
B(E)CDA-OMe pentasaccharide 2 after conventional
hydrogenolysis (76%).
The strategy described here demonstrates the advantage
of using BF3·OEt2 as the Lewis acid instead of
TMSOTf when using ‘bulky’ trichloroacetamidate
donors. Moreover, it shows that, as demonstrated ear-
lier in the S. flexneri Y series, the CD linkage is a
suitable position to target in the construction of
oligosaccharides of higher order in the S. flexneri 2a
series.31,32
4. Experimental
4.1. General methods
Melting points were determined in capillary tubes with
an electrothermal apparatus and are uncorrected. Opti-
cal rotations were measured for CHCl3 solutions at
25°C with a Perkin–Elmer automatic polarimeter,
model 241 MC. TLC on precoated slides of silica gel 60
F254 (Merck) was performed with solvent mixtures of
appropriately adjusted polarity consisting of A, cyclo-
hexane–acetone; B, cyclohexane–EtOAc; C, toluene–
acetone; D, CH2Cl2–MeOH; E, iso-propanol–
ammonia–water; F, water–acetonitrile. Detection was
effected when applicable, with UV light, and/or by
charring with orcinol (35 mM) in aqueous H2SO4 (4N).
Preparative chromatography was performed by elution
from columns of silica gel 60 (particle size 0.040–0.063
mm). Reverse-phase column chromatography was per-
formed by elution from columns of Lichoprep® RP-18
(25–40 mm). The NMR spectra were recorded at 25°C
Scheme 4. Reagents and conditions: (a) i. PhC(OMe)3, CSA, CH2Cl2, ii. 50% aq. TFA, CH2Cl2; (b) TMSOTf cat., Et2O,
−78“–30°C (97%); (c) PdCl2, NaOAc, AcOH, rt (75%); (d) CCl3CN, DBU cat., CH2Cl2 (83%); (e) BF3·OEt2, Et2O, −78“–30°C
(81%); (f) MeONa cat., MeOH/CH2Cl2 (90%); (g) 50% aq. TFA (82% (g+f)); (h) H2, Pd/C, MeOH/AcOH (76%).

2216
F. Segat-Dioury, L. A. Mulard / Tetrahedron: Asymmetry 13 (2002) 2211–2222
for solutions in CDCl3, unless stated otherwise, on a
phy of the residue (solvent B, 7:3“1:1) gave the b-
anomer 13 (50 mg, 8%) as the first isolated product and
the desired a-anomer 12 (466 mg, 80%) as a white
1
Bruker AC 300P spectrometer (300 MHz for H, 75
MHz for 13C). External references: for solutions in
CDCl3, TMS (0.00 ppm for both 1H and 13C); for
solutions in D2O, dioxane (67.4 ppm for 13C) and
trimethylsilyl-3 propionic acid sodium salt (0.00 ppm
1
foam; [h]D −15 (c 1.0); H NMR: l 7.39–7.30 (m, 10H,
Ph), 5.68 (d, 1H, JNH,2=7.5 Hz, NH), 5.28 (dd, 1H,
J2,3=3.4, J3,4=10.1 Hz, H-3C), 5.06 (dd, 1H, H-2C),
1
for H). Proton-signal assignments were made by first-
5.03 (pt, 1H, H-4C), 4.87 (d, 1H, J=10.8 Hz, OCH2),
4.80 (d, 1H, J1,2=8.4 Hz, H-1D), 4.73 (d, 1H, J1,2=1.4
Hz, H-1C), 4.68 (d, 1H, J=11.2 Hz, OCH2), 4.65 (d,
1H, J1,2=1.4 Hz, H-1A), 4.62 (d, 1H, OCH2), 4.60 (d,
1H, OCH2), 4.16 (dq, 1H, J4,5=9.9 Hz, H-5C), 3.97 (pt,
1H, J2,3=J3,4=9.5 Hz, H-3D), 3.89–3.83 (dd, 1H,
order analysis of the spectra, as well as analysis of
1
two-dimensional H–1H correlation maps (COSY) and
selective TOCSY experiments. Of the two magnetically
non-equivalent geminal protons at C-6 of the glucopy-
ranosyl moieties, the one resonating at lower field is
denoted H-6a and the one at higher field is denoted
H-6b. Abbreviations are as follows: p, b, s, d, t, q stand
for pseudo, broad, singlet, doublet, triplet, and quadru-
plet, respectively. The 13C NMR assignments were sup-
ported by two-dimensional 13C–1H correlation maps
(HETCOR). Interchangeable assignments are marked
with an asterisk in the listing of signal assignments.
Sugar residues in oligosaccharides are serially lettered
according to the lettering of the repeating unit of the
O-SP and identified by a subscript in the listing of
signal assignments. Fast atom bombardment mass spec-
tra (FABMS) were recorded in the positive-ion mode
J
5,6a=5.4, J6a,6b=10.8 Hz, H-6aD), 3.86–3.73 (m, 3H,
H-2A, 3A, 6bD), 3.64 (dq, 1H, H-5A), 3.60 (pt, 1H,
J
J
4,5=9.3 Hz, H-4D), 3.50 (m, 1H, H-2D), 3.68 (pt, 1H,
3,4=J4,5=9.3 Hz, H-4A), 3.30 (s, 3H, OCH3), 3.25 (m,
1H, H-5D), 2.13, 2.04, 1.99, 1.78 (4s, 12H, C(O)CH3),
1.50, 1.40 (2s, 6H, C(CH3)2), 1.32 (d, 3H, J5,6=6.2 Hz,
H-6A), and 1.16 (d, 3H, J5,6=6.2 Hz, H-6C); 13C NMR:
l 171.2–170.0 (4C, C(O)), 138.4–138.1 (Ph), 102.3 (C-
1D, JC,H=163 Hz), 100.1 (C-1A, JC,H=171 Hz), 99.4
(C(CH3)2), 97.7 (C-1C, JC,H=173 Hz), 80.8 (C-4A), 79.6
(C-3A), 77.4 (2C, C-2A, 3D), 75.5, 73.0 (2C, OCH2), 72.7
(C-4D), 71.4 (C-4C), 70.6 (C-2C), 68.9 (C-3C), 67.6 (C-
5A), 67.4 (C-5D), 66.3 (C-5C), 62.3 (C-6D), 57.8 (C-2D),
54.6 (OCH3), 29.2 (C(CH3)2), 23.4, 21.0, 20.9, 20.8, (4C,
C(O)CH3), 19.3 (C(CH3)2), 17.9 (C-6A), and 17.3 (C-
6C). ESMS for C44H59NO17 (M, 873.38) m/z 874.5
[M+H]+. Anal. calcd for C44H59NO17: C, 60.47; H, 6.80;
N, 1.60. Found: C, 60.39; H, 6.92; N, 1.64%.
using dithioerythritol/dithio-L-threitol (4/1, MB) as the
matrix, in the presence of NaI, and Xenon as the gas.
Anhydrous CH2Cl2, sold on molecular sieves, was used
as such. Et2O and THF were distilled over sodium/ben-
zophenone. CH3CN, suitable for DNA synthesis and
kept on Trap-Pack molecular sieves bags, was used as
such. Solutions in organic solvents were dried by pass-
ing through phase separator filters.
4.2.1. Available analytical data for 13. 1H NMR: l
7.40–7.20 (m, 10H, Ph), 5.55 (d, 1H, JNH,2=7.5 Hz,
NH), 5.50 (bd, 1H, J2,3=2.6 Hz, H-2C), 5.01 (pt, 1H,
J3,4=J4,5=9.1 Hz, H-4C), 4.96 (d overlapped, 1H, H-
1D), 4.94 (dd overlapped, 1H, H-3C), 4.87 (d, 1H,
4.2. Methyl (2,3,4-tri-O-acetyl-a-L-rhamnopyranosyl)-
(1“3)-(2-acetamido-2-deoxy-4,6-O-isopropylidene-b-
D
-
glucopyranosyl)-(1“2)-3,4-di-O-benzyl-a-
L
-rhamno-
pyranoside, 12
J=10.8 Hz, OCH2), 4.75 (bs, 1H, H-1C), 4.66 (d, 1H,
J
J
1,2=1.5 Hz, H-1A), 4.63 (m, 3H, OCH2), 4.20 (pt, 1H,
2,3=J3,4=9.5 Hz, H-3D), 3.90–3.77 (m, 4H, H-2A, H-
(a) A 0.1 M solution of TMSOTf in anhydrous Et2O
(250 mL, 271 mmol) was added at −78°C to a stirred
solution of the rhamnosyl donor23 11 (158 mg, 364
mmol) and the disaccharide acceptor15 4 (105 mg, 175
mmol) in Et2O (10 mL). The mixture was stirred at this
temperature for 7 h while the bath temperature reached
4°C, and was stirred at this temperature overnight.
Although TLC (solvent C, 4:1) showed some 4 still
remained, Et3N (20 mL) was added and after 15 min,
the suspension was concentrated. Chromatography of
the residue (solvent B, 7:3“1:1) gave first the a-anomer
13 (42 mg, 28%) as a white foam and then the b-
anomer 12 (20 mg, 13%).
6aD, 3A, 6bD), 3.63 (dq, 1H, J4,5=9.4 Hz, H-5A), 3.55
(pt, 1H, J4,5=9.4 Hz, H-4D), 3.47 (dq, 1H, H-5C), 3.44
(pt, 1H, J3,4=9.5 Hz, H-4A), 3.35 (m, 1H, H-2D), 3.30
(s, 3H, OCH3), 3.25 (m, 1H, H-5D), 2.14, 2.06, 1.99,
1.74 (4s, 12H, C(O)CH3), 1.49, 1.45 (2s, 6H, C(CH3)2),
1.31 (d, 3H, J5,6=6.2 Hz, H-6A), and 1.24 (d, 3H,
J
5,6=6.2 Hz, H-6C); 13C NMR: l 170.5, 170.2, 170.0
(4C, C(O)), 138.5–127.0 (Ph), 102.3 (C-1D, JC,H=156
Hz), 100.2 (C-1A, JC,H=175 Hz), 99.8 (C(CH3)2), 99.0
(C-1C, JC,H=164 Hz), 80.4 (C-4A), 79.5 (C-3A), 77.6
(C-3D), 76.8 (C-2A), 75.3 (OCH2), 74.0 (C-4D), 72.4
(OCH2), 71.1 (C-3C), 70.6 (C-4C), 70.4 (C-5C), 69.2
(C-2C), 67.8 (C-5A), 66.6 (C-5D), 62.1 (C-6D), 56.7 (C-
2D), 54.6 (OCH3), 28.9 (C(CH3)2), 23.5, 20.8, 20.7 (4C,
C(O)CH3), 18.9 (C(CH3)2), 17.9 (C-6A), and 17.7 (C-
6C). ESMS for C44H59NO17 (M, 873.38) m/z 834 [M−
C(CH3)2+3H]+.
,
(b) Activated powdered 4 A molecular sieves (1 g) were
added to a solution of the disaccharide acceptor 4 (402
mg, 0.67 mmol) and the rhamnopyranosyl donor 11
(523 mg, 1.2 mmol) in anhydrous Et2O (35 mL) and the
suspension was stirred for 30 min at −78°C. BF3·OEt2
(700 mL, 5.5 mmol) was added and the mixture was
stirred for 5 h while the bath temperature was slowly
coming back to 0°C. TLC (solvent B, 3:2) showed that
no 4 remained. Et3N (2.0 mL) was added and after 30
min, the suspension was filtered through a pad of
Celite. Concentration of the filtrate and chromatogra-
4.3. Methyl (2,3,4-tri-O-acetyl-a-
(1“3)-(2-acetamido-2-deoxy-b- -glucopyranosyl)-(1“
2)-3,4-di-O-benzyl-a- -rhamnopyranoside, 14
L-rhamnopyranosyl)-
D
L
50% aq. TFA (10 mL) was added at 0°C to a solution
of the fully protected trisaccharide 12 (450 mg, 515

F. Segat-Dioury, L. A. Mulard / Tetrahedron: Asymmetry 13 (2002) 2211–2222
2217
mmol) in CH2Cl2 (10 mL) and the mixture was stirred
at this temperature for 1.25 h. TLC (solvent D, 19:1)
showed that no starting 12 remained. The organic
phase was separated, washed successively with a satd
aq. solution of NaHCO3, water, and a satd aq. solu-
tion of NaCl, then concentrated. Chromatography of
the residue (solvent D, 39:1) gave diol 14 (410 mg,
4.5. Methyl a-
2-deoxy-b- -glucopyranosyl)-(1“2)-a-
rhamnopyranoside, 3
L-rhamnopyranosyl-(1“3)-(2-acetamido-
D
L-
10% Pd–C catalyst (100 mg) was added to a degassed
solution of the pentaol 15 (146 mg, 206 mmol) in a
mixture of methanol (9 mL) and acetic acid (1 mL).
The suspension was saturated with hydrogen at atmo-
spheric pressure and stirred overnight at rt. The mix-
ture was filtered on a pad of Celite and the crude
material was purified by reverse-phase chromatogra-
phy (solvent F, 100:0“49:1) to give the trisaccharide
3 as a lyophilized powder (89 mg, 82%). Analytical
data were as described.14 [h]D −51 (c 0.65, MeOH).
1H NMR: (D2O); l 4.79 (d, 1H, J1,2=1.8 Hz, H-1C),
1
95%) as a white foam; [h]D +4 (c 1.0); H NMR: l
7.37–7.30 (m, 10H, Ph), 5.87 (d, 1H, JNH,2=7.2 Hz,
NH), 5.26 (dd, 1H, J2,3=3.3, J3,4=10.1 Hz, H-3C),
5.15 (dd, 1H, H-2C), 5.09 (pt, 1H, J4,5=10.0 Hz, H-
4C), 4.90 (d, 1H, J1,2=8.4 Hz, H-1D), 4.88 (d, 1H,
J=10.8 Hz, OCH2), 4.79 (d, 1H, J1,2=1.4 Hz, H-1C),
4.72 (d, 1H, J1,2=1.4 Hz, H-1A), 4.70 (d, 1H, J=11.4
Hz, OCH2), 4.63 (d, 1H, OCH2), 4.61 (d, 1H, OCH2),
4.14 (dq, 1H, H-5C), 3.95 (pt, 1H, J2,3=8.3 Hz, H-
3D), 3.91 (m, 1H, H-2A), 3.86 (m, 2H, H-6aD, 6bD),
3.81 (m, 1H, H-3A), 3.66 (dq, 1H, J4,5=9.4 Hz, H-
5A), 3.55 (pt, 1H, J3,4=J4,5=8.9 Hz, H-4D), 3.36 (m,
3H, H-4A, 2D, 5D), 3.31 (s, 3H, OCH3), 2.15, 2.05,
1.99, 1.81 (4s, 12H, C(O)CH3), 1.33 (d, 3H, J5,6=6.2
Hz, H-6A), and 1.16 (d, 3H, J5,6=6.2 Hz, H-6C); 13C
NMR: l 171.1–170.1, 170.0 (4C, C(O)), 138.4–127.7
(Ph), 101.5 (C-1D), 100.0 (C-1A), 99.1 (C-1C), 83.5 (C-
3D), 80.7 (C-4A), 79.5 (C-3A), 77.1 (C-2A), 75.4
(OCH2), 75.3 (C-5D), 72.7 (OCH2), 70.7 (C-4C), 70.1
(C-4D), 69.9 (C-2C), 68.8 (C-3C), 67.7 (C-5A), 67.5 (C-
5C), 62.2 (C-6D), 56.6 (C-2D), 54.6 (OCH3), 23.4, 21.0,
20.8, (4C, C(O)CH3), 19.0 (C-6A), and 17.5 (C-6C).
FABMS for C41H55NO17 (M, 833.35) m/z 856.4 [M+
Na]+. Anal. calcd for C41H55NO17: C, 59.05; H, 6.65;
N, 1.68. Found: C, 58.91; H, 6.79; N, 1.52%.
4.77 (d, 1H, J1,2=1.6 Hz, H-1A), 4.67 (d, 1H, J1,2
7.9 Hz, H-1D), 3.93 (dd, 1H, J2,3=3.2 Hz, H-2A), 3.91
(dq, 1H, J4,5=9.0 Hz, H-5C), 3.84 (dd, 1H, J5,6a=2.2,
=
J6a,6b=12.2 Hz, H-6aD), 3.75 (dd, 1H, J2,3=10.1 Hz,
H-2D), 3.74–3.65 (m, 4H, H-2C, 3A, 6bD, 3C), 3.60
(dq, partially overlapped, 1H, J4,5=9.7 Hz, H-5A),
3.53 (pt, partially overlapped, 1H, H-3D), 3.44 (pt,
1H, J3,4=J4,5=8.6 Hz, H-4D), 3.39 (m, 1H, H-5D),
3.35 (pt, 1H, J3,4=9.7 Hz, H-4C), 3.31 (s, 3H, OCH3),
3.24 (pt, 1H, J3,4=9.7 Hz, H-4A), 2.00 (s, 3H,
C(O)CH3), 1.25 (d, 3H, J5,6=6.2 Hz, H-6A), and 1.16
(d, 3H, J5,6=6.2 Hz, H-6C); 13C NMR: (D2O); l
174.9 (C(O)), 102.2 (C-1D, JC–H=165 Hz), 101.6 (C-
1C, J=170 Hz), 100.0 (C-1A, JC–H=172 Hz), 81.5 (C-
3D), 78.9 (C-2A), 76.2 (C-5D), 72.6 (C-4A), 72.2
(C-4C), 71.1 (C-2C), 70.5 (C-3C), 70.3 (C-3A), 69.3 (C-
5C), 68.9 (C-5A), 68.7 (C-4D), 61.0 (C-6D), 56.0 (C-
2D), 55.2 (OCH3), 22.6 (C(O)CH3), 17.0 (C-6A), 16.8
(C-6C). High-resolution ESMS for C21H37NO14 (M+
Na, 550.21117) m/z 550.21040 [M+Na]+.
4.4. Methyl a-
2-deoxy-b- -glucopyranosyl)-(1“2)-3,4-di-O-benzyl-a-
rhamnopyranoside, 15
L-rhamnopyranosyl-(1“3)-(2-acetamido-
D
L-
Methanolic MeONa (1 M) was added to a solution
of diol 14 (299 mg, 359 mmol) in a 1:1 mixture of
CH2Cl2 and MeOH (5 mL) until the pH reached 10.
The mixture was stirred overnight at rt and neutral-
ized with Amberlite IR-120 (H+). The crude material
was purified by column chromatography (solvent D,
10:1) to give the pentanol 15 (250 mg, 98%) as a
4.6. Allyl (2,3,4,6-tetra-O-benzyl-a-
(1“4)-2,3-O-isopropylidene-a- -rhamnopyranoside, 18
D-glucopyranosyl)-
L
TMSOTf (40 mL, 0.02 equiv.) was added to a solu-
tion of the rhamnose acceptor21 10 (2.74 g, 11.2
mmol) in anhydrous Et2O (20 mL) and the mixture
was stirred at −78°C for 15 min. A solution of the
glucopyranosyl donor19,20 9 (9.49 g, 13.9 mmol) in a
mixture of CH2Cl2 (10 mL) and Et2O (80 mL) was
added dropwise for 3.5 h while the bath was slowly
coming back to −55°C. The mixture was stirred for 3
h more, at which time TLC (solvent A, 1:1) showed
the total disappearance of 10. Et3N (150 mL) was
added, and the mixture was stirred for 0.5 h, then
volatiles were evaporated. Chromatography of the
residue (solvent A, 19:1) gave first a mixture of the
condensation products 18 and 19 in a ꢀ3:2 ratio
(3.28 g, 38%), then the pure a-disaccharide 18 (4.38 g,
50.9%). In an analogous experiment run on 4.78 g
(18.6 mmol) of acceptor 10, repeated chromatography
(solvents A and C) of the crude reaction mixture
yielded 11.03 g (73%) of the pure a-anomer 18. Ana-
lytical data for 18, isolated as a colourless oil, were
identical to that reported previously.12
1
white foam; [h]D −25 (c 1.0); H NMR: (DMSO-d6);
l 7.70 (d, 1H, JNH,2=8.4 Hz, NH), 7.43–7.27 (m,
10H, Ph), 4.87–4.50 (m, 12H, H-1C, 1D, 1A, OH,
OCH2), 4.01 (bs, 1H, H-2A), 3.86 (dq, 1H, J4,5=9.4,
J5,6=6.2 Hz, H-5C), 3.70 (dd, 1H, J6a,6b=11.3, J5,6a=
9.3, H-6aD), 3.61 (dd, 1H, J2,3=2.8, J3,4=9.2 Hz, H-
3A), 3.59–3.50 (m, 4H, H-3D, 2D, 2C, 6bD), 3.48–3.30
(m, 6H, H-5A, 3C, 4A, OCH3), 3.21–3.14 (m, 3H, H-
5D, 4C, 4D), 2.50 (s, 3H, C(O)CH3), and 1.10 (m, 6H,
H-6A, 6C); 13C NMR: (DMSO-d6); l 169.0 (C(O)),
138.7–127.3 (Ph), 102.2 (C-1D), 101.0 (C-1C), 99.6 (C-
1A), 80.1 (C-3D), 79.1 (C-4A), 78.6 (C-3A), 76.6 (C-
5D*), 74.8 (C-2A), 74.1 (OCH2), 71.9 (C-4C*), 70.6
(C-2C), 70.5 (C-3C), 70.0 (OCH2), 69.1 (C-4D*), 68.3
(C-5A), 67.0 (C-5C), 61.0 (C-6D), 55.2 (C-2D), 54.0
(OCH3), 23.0 (C(O)CH3), 17.9 (2C, C-6A, 6C).
FABMS for C35H49NO14 (M, 707.32) m/z 730.4 [M+
Na]+. Anal. calcd for C35H49NO14: C, 59.39; H, 6.98;
N, 1.98. Found: C, 59.22; H, 7.15; N, 1.85%.

2218
F. Segat-Dioury, L. A. Mulard / Tetrahedron: Asymmetry 13 (2002) 2211–2222
4.8. Methyl (2,3,4,6-tetra-O-benzyl-a-
osyl)-(1“4)-(2,3-di-O-benzoyl-a- -rhamnopyranosyl)-
(1“3)-(2-acetamido-2-deoxy-b- -glucopyranosyl)-(1“
2)-3,4-di-O-benzyl-a- -rhamnopyranoside, 22
D-glucopyran-
4.7. Methyl (2,3,4,6-tetra-O-benzyl-a-D-glucopyran-
L
osyl)-(1“4)-(2,3-di-O-benzoyl-a-L-rhamnopyranosyl)-
D
(1“3)-(2-acetamido-2-deoxy-4,6-O-isopropylidene-b-D-
L
glucopyranosyl)-(1“2)-3,4-di-O-benzyl-a-L-
rhamnopyranoside, 20
A solution of the fully protected tetrasaccharide 20
(1.95 g, 1.32 mmol) in CH2Cl2 (25 mL) was treated,
at 0°C, with 50% aq. TFA (25 mL) for 2 h. Solid
Na2CO3 (10 g) was added portionwise to the reaction
mixture to which CH2Cl2 (25 mL) had been added.
The organic phase was separated and washed with a
2 M aq. solution of Na2CO3, then with a satd aq.
solution of NaCl. Evaporation of the volatiles and
chromatography (solvent B, 1:1) of the residue gave
diol 22 (1.75 g, 92%) as a white foam; [h]D +79 (c
1.0); 1H NMR: l 8.03–7.01 (m, 40H, Ph), 5.87 (d,
1H, JNH,2=7.1 Hz, NH), 5.60 (dd, 1H, J2,3=3.4,
(a) A 0.11 M ethereal solution of TMSOTf (250 mL,
27 mmol) was added, at −78°C, to a mixture of the
disaccharide acceptor15 4 (105 mg, 175 mmol) and the
disaccharide donor12 5 (307 mg, 295 mmol) in anhy-
drous Et2O (11 mL). The mixture was stirred at 4°C
for 7 h, at which time Et3N (20 mL, 142 mmol) was
added, and the mixture was concentrated. Column
chromatography of the residue (solvent B, 4:1) gave
the expected tetrasaccharide 20 (71 mg, 27%, cor-
rected yield 41%), then the supposedly corresponding
b-glycosidation product 21 (19 mg, 7%, corrected
yield 11%), and finally the unreacted acceptor 4 (36
mg, conversion rate 65%). ESMS data for 21 m/z
1479 [M+H]+corresponded to C86H95NO21 (M,
1478.71).
J3,4=9.1 Hz, H-3C), 5.48 (dd, 1H, J1,2=2.2 Hz, H-
2C), 5.06 (d, 1H, J1,2=8.3 Hz, H-1D), 4.95 (m, 2H,
H-1C, 1E), 4.74 (bs, 1H, H-1A), 4.90–4.60 (m, 9H,
OCH2), 4.35 (d, 1H, J=11.0 Hz, OCH2), 4.37–4.18
(m, 3H, H-5C, 3D, OCH2), 3.96–3.83 (m, 7H, H-2A,
3E, 6aD, 6bD, OCH2, 4C, 3A), 3.72–3.56 (m, 4H, H-5E,
5A, 4E, 4D), 3.50 (dd, 1H, J1,2=3.3, J2,3=9.7 Hz, H-
2E), 3.45 (pt, 1H, J3,4=J4,5=9.7 Hz, H-4A), 3.43–3.35
(m, 2H, H-2D, 5D), 3.32 (m, 4H, H-6aE, OCH3), 3.06
(b) BF3·OEt2 (1.3 mL, 10.3 mmol) was added por-
tionwise, at −78°C, to a mixture of the disaccharides
4 (825 mg, 1.37 mmol) and 5 (2.21 g, 2.13 mmol) in
anhydrous Et2O (50 mL) containing activated pow-
(bd, 1H,
J6a,6b=10.6 Hz, H-6bE), 1.81 (s, 3H,
,
ered 4 A molecular sieves (2 g). The mixture was
C(O)CH3), 1.51 (d, 3H, J5,6=6.0 Hz, H-6C), and 1.35
(d, 3H, J5,6=6.2 Hz, H-6A); 13C NMR: l 171.1,
165.5, 165.3 (3C, C(O)), 138.8–127.4 (Ph), 101.2 (C-
1D), 100.2 (C-1A), 99.5 (2C, C-1C, 1E), 84.2 (C-3D),
81.7 (C-3E), 80.6 (C-4A), 80.2 (C-2E), 79.5 (C-3A), 79.3
(C-4C), 77.3 (C-4E), 77.0 (C-2A), 75.6, 75.5 (2C,
OCH2), 75.2 (C-5D), 74.7, 74.1, 73.3, 72.4 (4C,
OCH2), 71.3 (C-5E), 70.8 (C-4D), 70.7 (C-3C), 70.6
(C-2C), 69.0 (C-5C), 67.7 (C-5A), 67.6 (C-6E), 62.7 (C-
6D), 57.1 (C-2D), 54.7 (OCH3), 23.4 (C(O)CH3), 18.5
(C-6C), and 17.1 (C-6A). ESMS for C83H91NO21 (M,
1437.61) m/z 1438.5 [M+H]+. Anal. calcd for
C83H91NO21: C, 69.30; H, 6.38; N, 0.97. Found: C,
69.15; H, 6.42; N, 1.01%.
stirred for 3 h while the cooling bath was slowly
coming back to −10°C. TLC (solvent B, 2.3:1)
showed the complete disappearance of 4. Et3N (4 mL,
28.7 mmol) was added and after 30 min, the mixture
was filtered through a pad of Celite, and the filtrate
was concentrated. Chromatography of the residue
(solvent B, 4:1) gave 20 (1.78 g, 88%) as a white
foam; [h]D +85 (c 1.0); 1H NMR: l 8.05–7.01 (m,
40H, Ph), 5.80 (d, 1H, JNH,2=7.4 Hz, NH), 5.61 (dd,
1H, J2,3=3.5, J3,4=9.5 Hz, H-3C), 5.39 (dd, 1H,
J
1,2=1.7 Hz, H-2C), 5.00 (d, 1H, J1,2=3.3 Hz, H-1E),
4.94 (d, 1H, J1,2=8.4 Hz, H-1D), 4.92 (bs, 1H, H-1C),
4.69 (bs, 1H, H-1A), 4.91–4.62 (m, 9H, OCH2), 4.34
(d, 1H, J=10.9 Hz, OCH2), 4.32–4.20 (m, 3H, H-5C,
3D, OCH2), 3.95–3.79 (m, 7H, H-6aD, 3E, 4C, 2A,
OCH2, 3A, 6bD), 3.68–3.61 (m, 4H, H-5E, 5A, 4E, 4D),
3.53–3.39 (m, 3H, H-2E, 2D, 4A), 3.39–3.25 (m, 5H,
H-5D, 6aE, OCH3), 3.05 (bd, 1H, J6a,6b=10.9 Hz, H-
6bE), 1.78 (s, 3H, C(O)CH3), 1.49 (s, 3H, C(CH3)2),
4.9. Methyl (2,3,4,6-tetra-O-benzyl-a-
osyl)-(1“4)-a- -rhamnopyranosyl-(1“3)-(2-acetamido-
2-deoxy-b- -glucopyranosyl)-(1“2)-3,4-di-O-benzyl-
a- -rhamnopyranoside, 23
D-glucopyran-
L
D
L
1.43 (d, 3H,
J5,6=6.0 Hz, H-6C), 1.35 (s, 3H,
Methanolic MeONa (1 M) was added dropwise to a
solution of diol 22 (700 mg, 487 mmol) in a mixture
of CH2Cl2 (2 mL) and MeOH (2 mL) until the pH
reached 10, and the mixture was stirred overnight at
rt. TLC showed that 22 had turned into a more polar
product. After neutralization with Amberlite IR-120
(H+), filtration and evaporation of the solvent, the
crude product was purified by column chromatogra-
phy (solvent D, 32:1) to give the tetraol 23 (589 mg,
C(CH3)2), and 1.34 (d, 3H, J5,6=6.3 Hz, H-6A); 13C
NMR: l 171.3, 165.5, 165.4 (3C, C(O)), 138.7–127.4
(Ph), 102.0 (C-1D, JC–H=164 Hz), 100.1 (C-1A, JC–H
=
171 Hz), 99.5 (C(CH3)2), 99.1 (C-1E, JC–H=167 Hz),
97.5 (C-1C, JC–H=172 Hz), 81.6 (C-3E), 80.7 (C-4A),
80.4 (C-2E), 79.6 (C-3*A), 79.5 (C-4C*), 77.3 (2C, C-4E,
2A), 77.0 (C-3D), 75.5, 75.4, 74.6, 74.0, 73.3 (5C,
OCH2), 72.8 (C-4D), 72.7 (OCH2), 71.4 (C-2C), 71.2
(C-5E), 71.1 (C-3C), 67.7 (C-5A), 67.6 (C-6E), 67.5 (C-
5C), 67.3 (C-5D), 62.3 (C-6D), 58.4 (C-2D), 54.5
(OCH3), 29.1 (C(CH3)2), 23.4 (C(O)CH3), 19.3
(C(CH3)2), 18.2 (C-6C), and 17.8 (C-6A). ESMS for
C86H95NO21 (M, 1478.71) m/z 1479 [M+H]+. Anal.
calcd for C86H95NO21: C, 69.85; H, 6.48; N, 0.95.
Found: C, 69.75; H, 6.56; N, 0.97%.
1
98%) as a white foam; [h]D +38 (c 1.0); H NMR: l
7.40–7.14 (m, 30H, Ph), 5.61 (d, 1H, JNH,2=7.5 Hz,
NH), 4.97–4.39 (m, 12H, OCH2), 4.88 (d, partially
overlapped, 1H, J1,2=4.2 Hz, H-1E), 4.75 (bs, 1H,
H-1C), 4.72 (bs, 1H, H-1A), 4.60 (d, partially over-
lapped, 1H, J1,2=8.0 Hz, H-1D), 4.07–3.78 (m, 9H,
H-5E, 3E, 5C, 2A, 6aD, 3A, 2C, 3C, 6bD), 3.72–3.44 (m,

F. Segat-Dioury, L. A. Mulard / Tetrahedron: Asymmetry 13 (2002) 2211–2222
2219
8H, H-5A, 2D, 6aE, 6bE, 2E, 4E, 4D, 3D), 3.42–3.33 (m, 6H,
H-4A, 4C, 5D, OCH3), 2.91 (bs, 1H, OH), 2.27 (bs, 1H,
OH), 1.73 (s, 3H, C(O)CH3), 1.41 (d, 3H, J5,6=6.2 Hz,
H-6C), and 1.33 (d, 3H, J5,6=6.2 Hz, H-6A); 13C NMR:
l 170.2 (C(O)), 138.5–127.6 (Ph), 102.5 (C-1D), 101.3
(C-1C), 100.0 (C-1A), 99.1 (C-1E), 86.1 (C-3D), 84.3 (C-4*A),
81.6 (C-3E), 81.0 (C-4C*), 79.9 (C-3A), 79.7 (C-2E*), 77.7
(C-4E*), 77.4 (C-2A), 75.7 (OCH2), 75.5 (C-5D), 75.4, 74.9,
73.6, 73.5, 73.2 (OCH2), 71.2 (C-5E), 70.8 (C-2C), 70.3
(C-4D), 69.4 (C-3C), 68.6 (C-6E), 67.9 (C-5C), 67.7 (C-5A),
62.6 (C-6D), 55.3 (C-2D), 54.6 (OCH3), 23.4 (C(O)CH3),
17.8 (C-6A), and 17.7 (C-6C). FABMS for C69H83NO19
(M, 1229.56) m/z 1252.6 [M+Na]+. Anal. calcd for
C69H83NO19: C, 67.36; H, 6.80; N, 1.14. Found: C, 67.25;
H, 6.95; N, 0.95%.
(60 mg, 2.58 mmol) for 2 h at rt, then cooled to 0°C. 50%
aq. TFA (11 mL) was added and the biphasic mixture
was stirred for 50 min at this temperature. At this time
TLC (solvent B, 2.5:1) showed that no intermediate
orthoester remained. The mixture was treated with Et3N,
volatiles were evaporated, and the residue was purified
bycolumnchromatography(solventB, 9:1containing1‰
Et3N) to give 24 as a white foam (5.91 g, 87%); [h]D +32
(c 1.0); 1H NMR: l 8.16–7.19 (m, 25H, Ph), 5.99 (m, 1H,
CHꢀCH2), 5.49 (m, 1H, H-2C), 5.49–5.28 (m, 2H,
CHꢀCH2), 5.05 (d, 1H, J1,2=3.6 Hz, H-1E), 5.04 (d, 1H,
J=10.6 Hz, OCH2), 5.00 (d, 1H, J1,2=1.2 Hz, H-1C),
4.93–4.75 (m, 3H, OCH2), 4.64–4.49 (m, 4H, OCH2),
4.30–4.16 (m, 4H, OCH2, H-3C, 6aE, 6bE), 4.11–4.04 (m,
2H, H-3E, OCH2), 3.96 (dq, 1H, J4,5=9.3 Hz, H-5C),
3.74–3.62 (m, 3H, H-2E, 4E, 5E), 3.58 (pt, 1H, J3,4=9.3
Hz, H-4C), and 1.54 (d, 3H, J5,6=6.2 Hz, H-6C); 13C
NMR: l 166.0 (C(O)), 138.7–127.7 (Ph, All), 117.7 (All),
98.7 (C-1E), 96.6 (C-1C), 85.4 (C-4C), 81.7 (C-3E), 80.1
(C-4E), 77.8 (C-5E), 75.7, 75.2, 73.8, 73.5 (4C, OCH2), 72.7
(C-2C), 71.3 (C-3C), 68.5 (2C, C-2E, 6E), 68.3 (OCH2), 66.7
(C-5C), and 18.1 (C-6C). ESMS for C50H54O11 (M, 830.37)
m/z 831.4 [M+H]+. Anal. calcd for C50H54O11·H2O: C,
70.74; H, 6.65. Found: C, 70.80; H, 6.56%.
4.10. Methyl a-
ranosyl-(1“3)-2-acetamido-2-deoxy-b-
(1“2)-a- -rhamnopyranoside, 1
D
-glucopyranosyl-(1“4)-a-
L-rhamnopy-
D
-glucopyranosyl-
L
The benzylated tetrasaccharide 23 (484 mg, 394 mmol) was
dissolved in a mixture of methanol (10 mL) and AcOH
(1 mL), treated with 10% Pd–C catalyst (200 mg), and
the suspension was stirred overnight at rt under an
atmospheric pressure of hydrogen. TLC monitoring
(solventD, 3:2)showedthatthestartingmaterialhadbeen
transformed into a more polar product. The suspension
was filtered on a pad of Celite. The filtrate was concen-
trated and coevaporated repeatedly with cyclohexane.
Reverse-phase chromatography of the residue (solvent F,
100:0“49:1), followed by freeze-drying, gave the targeted
tetrasaccharide 1 as an amorphous powder (230 mg, 85%);
4.12. Allyl (2-O-acetyl-3,4-di-O-benzyl-a-
L
-rhamno-
-gluco-
pyranosyl)-(1“3)-[(2,3,4,6-tetra-O-benzyl-a-
D
pyranosyl)-(1“4)]-2-O-benzoyl-a-L-rhamno-
pyranoside, 25
TMSOTf (180 mL, 99 mmol) was added to a solution of
donor22 8 (3.82 g, 7.2 mmol) and acceptor 24 (4.32 g, 5.2
mmol)inanhydrousEt2O(260mL)at−78°C. Themixture
was stirred for 3 h, at which time the bath temperature
was −30°C. As no starting acceptor remained, Et3N (800
mL) was added and the mixture was stirred for 15 min.
Evaporation of the volatiles followed by column chro-
matography of the residue (solvent B, 1‰ Et3N) gave pure
1
[h]D +3 (c 1.0, water); H NMR: (D2O); l 5.04 (d, 1H,
J
1,2=3.8 Hz, H-1E), 4.87 (bs, 1H, H-1C), 4.84 (bs, 1H,
H-1A), 4.76 (d, overlapped, 1H, H-1D), 4.10 (dq, 1H,
4,5=9.5 Hz, H-5C), 4.01 (m, 1H, H-2A), 4.00 (m, 1H,
J
H-5E), 3.92 (dd, 1H, J6a,6b=12.0, J5,6a=1.8 Hz, H-6aD),
3.87–3.73 (m, 7H, H-3C, 3A, 6aE, 6bE, 2D, 2C, 6bD),
3.73–3.61 (m, 3H, H-3E, 3D, 5A), 3.59–3.43 (m, 5H, H-2E,
4D, 4C, 5D, 4E), 3.39 (s, 3H, OCH3), 3.32 (pt, 1H,
1
25 as a white foam (6.08 g, 97%); [h]D +24 (c 1.0); H
NMR: l 8.07–7.12 (m, 35H, Ph), 5.93 (m, 1H, CHꢀCH2),
5.70 (dd, 1H, J1,2=2.2 Hz, H-2C), 5.41 (dd, 1H, J2,3=3.1
Hz, H-2B), 5.33 (dd, 1H, J=17.2, J=1.5 Hz, CHꢀCH2),
5.24 (dd, 1H, J=10.3, J=1.3 Hz, CHꢀCH2), 5.04 (d, 1H,
J3,4=J4,5=9.6 Hz, H-4A), 2.07 (s, 3H, C(O)CH3), 1.32 (d,
3H, J5,6=6.2 Hz, H-6C), and 1.28 (d, 3H, J5,6=6.2 Hz,
H-6A); 13C NMR: (D2O); l 175.3 (C(O)), 102.7 (C-1D,
JC–H=163 Hz), 102.0 (C-1C, JC–H=170 Hz), 100.5 (2C,
J1,2=3.2 Hz, H-1E), 5.01 (d, 1H, J1,2=1.6 Hz, H-1C), 4.94
C-1A, 1E, JC–H=170 Hz), 82.3 (C-3D), 81.8 (C-4C), 79.3
(C-2A), 76.7 (C-4E), 73.6 (C-3E), 73.1 (C-4A), 72.6 (C-5E),
72.4 (C-2E), 71.8 (C-2C), 70.7 (C-3A), 70.1 (C-5D), 69.7
(C-3C), 69.3 (C-5A), 69.2 (C-4D), 68.9 (C-5C), 61.4 (C-6D),
60.9 (C-6E), 56.4 (C-2D), 55.6 (OCH3), 23.0 (C(O)CH3),
17.5 (C-6A), and 17.3 (C-6C). High-resolution ESMS for
C27H47NO19 (M−H, 688.26640) m/z 688.26880 [M−H]+.
(d, 1H, J=11.0 Hz, OCH2), 4.92 (d, 1H, J1,2=1.8 Hz,
H-1B), 4.91–4.78 (m, 5H, OCH2), 4.69–4.33 (m, 6H,
OCH2), 4.20–4.14 (m, 2H, H-3B, OCH2), 4.02 (m, 3H,
H-5E, 3E, OCH2), 3.89 (bd, 1H, J6a,6b=9.4 Hz, H-6aE),
3.83–3.70 (m, 5H, H-5B, 6bE, 4B, 4E, 3C), 3.64 (dq, 1H,
J
4,5=9.4 Hz, H-5C), 3.50 (dd, 1H, J2,3=9.5 Hz, H-2E),
3.31 (pt, 1H, J3,4=9.4 Hz, H-4C), 2.14 (s, 3H, C(O)CH3),
1.38 (d, 3H, J5,6=5.9 Hz, H-6B), and 0.99 (d, 3H, J5,6=6.2
Hz, H-6C); 13C NMR: l 170.1, 165.8 (2C, C(O)), 138.9–
127.4 (Ph, All), 117.8 (All), 99.4 (bs, C-1C, JC,H=169 Hz),
98.3 (C-1E), 96.1 (C-1B, JC,H=169 Hz), 81.9 (C-3E), 81.3
(C-2E), 79.9 (C-4C), 79.8 (bs, C-3B), 78.9 (C-4B), 77.9
(C-4E), 77.5 (C-3C), 75.7, 75.2, 75.0, 74.1, 73.0 (5C,
OCH2), 72.2(C-2B), 71.7(C-5E), 70.6(OCH2), 68.8(C-5C),
68.7 (C-2C), 68.6 (C-6E), 68.5 (OCH2), 67.5 (C-5B), 21.3
(C(O)CH3), 18.9 (C-6B), and 17.7 (C-6C). ESMS for
C72H78O16 (M, 1198.4) m/z 1199.5 [M+H]+. Anal. calcd
for C72H78O16: C, 72.10; H, 6.55. Found: C, 72.19; H,
6.49%.
4.11. Allyl (2,3,4,6-tetra-O-benzyl-a-
(1“4)-O-a- -rhamnopyranoside, 24
D-glucopyranosyl)-
L
A solution of the fully protected disaccharide 18 (6.27 g,
8.18 mmol) in 80% aq. AcOH (88 mL) was heated for
4.5 h at 70°C. TLC monitoring (solvent B, 2.5:1) showed
the presence of one more polar product. The mixture was
concentrated and coevaporated repeatedly with cyclohex-
ane and toluene. The resulting crude diol 7 (6.11 g) was
solubilized in anhydrous CH2Cl2 (20 mL) and treated with
trimethyl orthobenzoate (10 mL, 58.2 mmol) and CSA

2220
F. Segat-Dioury, L. A. Mulard / Tetrahedron: Asymmetry 13 (2002) 2211–2222
1.42 (d, 3H, J5,6=6.0 Hz, H-6C), and 0.98 (bs, 3H,
H-6B); 13C NMR: l 170.0, 165.5 (2C, C(O)), 160.3
(CꢀNH), 138.8–127.5 (Ph), 98.8 (bs, 2C, C-1B, 1E),
94.4 (bs, C-1C), 91.0 (CCl3), 81.8 (C-3E), 81.0 (bs,
C-2E), 79.7 (C-4B), 77.7 (C-4E*), 77.5 (C-3B*), 75.6,
75.2, 74.9, 74.1, 73.1 (5C, OCH2), 71.7 (C-5E), 71.0
(bs, OCH2), 70.8 (C-2C), 70.2 (bs, C-5C), 68.8 (bs,
C-5B), 68.6 (C-2B), 68.4 (C-6E), 21.2 (C(O)CH3), 18.8
(bs, C-6C), and 17.7 (C-6B). Due to signal broadness,
C-3C and C-4C could not be extracted from any of
the 1D or 2D spectra. Anal. calcd for
C71H74Cl3NO16: C, 65.41; H, 5.72; N, 1.07. Found: C,
65.26; H, 6.86; N, 1.02%.
4.13. (2-O-Acetyl-3,4-di-O-benzyl-a-
L
-rhamnopyran-
-gluco-
L-rhamno-
osyl)-(1“3)-[(2,3,4,6-tetra-O-benzyl-a-
D
pyranosyl)-(1“4)]-2-O-benzoyl-a/b-
pyranose, 26
Water (35 drops) was added to a suspension of palla-
dium dichloride (2.07 g, 11.66 mmol), sodium acetate
(3.41 g, 25 mmol) and the fully protected pentasac-
charide 25 (5.93 g, 4.95 mmol) in acetic acid (31.2
mL). The mixture was stirred overnight at rt. TLC
(solvent B, 2.3:1) showed that the starting material
had turned into
a major more polar product.
Volatiles were evaporated and the residue was taken
up in AcOEt and washed successively with satd aq.
NaHCO3, and satd aq. NaCl. Column chromatogra-
phy of the residue (solvent B, 4:1) gave pure hemiac-
4.15. Methyl (2-O-acetyl-3,4-di-O-benzyl-a-
pyranosyl)-(1“3)-[(2,3,4,6-tetra-O-benzyl-a-
glucopyranosyl)-(1“4)]-(2-O-benzoyl-a- -rhamno-
pyranosyl)-(1“3)-(2-acetamido-2-deoxy-4,6-O-
isopropylidene-b- -glucopyranosyl)-(1“2)-3,4-di-O-
benzyl-a- -rhamnopyranoside, 27
L-rhamno-
D
-
1
L
etal 26 (4.31 g, 75%) as a white foam; H NMR: l
8.06–7.12 (m, 35H, Ph), 5.68 (dd, 1H, J2,3=2.5 Hz,
H-2B), 5.39 (dd, 1H, H-2C), 5.21 (dd, 1H, J1,2=2.4
Hz, H-1C), 5.03 (d, 1H, H-1E), 5.01 (d, 1H, J1,2=1.8
Hz, H-1B), 4.98–4.40 (m, 11H, OCH2), 4.23 (dd, 1H,
D
L
BF3·OEt2 (1.25 mL, 9.86 mmol) was added to a mix-
ture of the disaccharide acceptor 4 (794 mg, 1.32
mmol) and the trisaccharide donor 6 (2.61 g, 2.0
mmol) in anhydrous Et2O (70 mL) containing acti-
J
2,3=3.2, J3,4=8.5 Hz, H-3C), 4.07–3.98 (m, 4H, H-
3E, 5C, 5E, OCH2), 3.89 (bd, 1H, J6a,6b=10.3 Hz, H-
6aE), 3.83–3.69 (m, 4H, H-6bE, 4E, 3B, 4C), 3.66 (dq,
1H, J4,5=9.5 Hz, H-5B), 3.50 (dd, 1H, J1,2=3.3,
,
vated powered 4 A molecular sieves (2 g) and the
J2,3=9.7 Hz, H-2E), 3.32 (pt, 1H, J3,4=9.4 Hz, H-4B),
mixture was processed as described for the prepara-
tion of 20. Chromatography of the residue (solvent B,
4:1“2.3:1) gave the fully protected pentasaccharide
27 (1.86 g, 81%) as a white foam; [h]D +26 (c 1.0);
1H NMR: l 8.04–7.10 (m, 45H, Ph), 5.72 (pt, 1H,
H-2C), 5.66 (d, 1H, JNH,2=7.4 Hz, NH), 5.25 (dd,
1H, J1,2=1.9 Hz, H-2B), 5.07 (d, 1H, J1,2=3.2 Hz,
H-1E), 5.02 (d, 1H, J1,2=1.6 Hz, H-1C), 4.97–4.33 (m,
16H, OCH2), 4.77 (bs, 2H, H-1D, 1B), 4.68 (bs, 1H,
H-1A), 4.11 (dd, 1H, J2,3=3.2, J3,4=9.1 Hz, H-3B),
4.07–3.93 (m, 3H, H-5B, 5E, 3E), 3.89–3.69 (m, 10H,
H-6aE, 2A, 3A, 6aD, 6bE, 6bD, 4B, 3C, 4E, 3D), 3.67–
3.04 (d, 1H, J1,OH=4.2 Hz, OH-1C), 2.13 (s, 3H,
C(O)CH3), 1.36 (d, 3H, J5,6=6.2 Hz, H-6C), and 0.99
(d, 3H, J5,6=6.2 Hz, H-6B); 13C NMR: l 170.2, 165.8
(2C, C(O)), 133.3–127.4 (Ph), 99.0 (C-1B), 98.4 (C-1E),
91.3 (C-1C), 81.9 (C-3E), 81.3 (C-2E), 79.9 (C-4B), 79.2
(C-4C), 79.1 (C-3C), 77.8 (C-4E), 77.3 (C-3B), 75.7,
75.3, 75.0, 74.0, 73.0 (5C, OCH2), 72.4 (C-2C), 71.6
(C-5E), 70.6 (OCH2), 68.7 (2C, C-5B, 2B), 68.5 (C-6E),
67.4 (C-5C), 21.3 (C(O)CH3), 18.9 (C-6C), and 17.7
(C-6B). ESMS for C69H74NO16 (M, 1158.50) m/z
1159.6 [M+H]+. Anal. calcd for C69H74NO16: C,
71.49; H, 6.62; N, 6.43. Found: C, 71.38; H, 6.47%.
3.60 (m, 3H, H-5A, 2D, 5C), 3.57 (pt, 1H, J3,4=J4,5
9.2 Hz, H-4D), 3.48 (dd, 1H, J2,3=9.6 Hz, H-2E), 3.42
(pt, 1H, 3,4=J4,5=9.3 Hz, H-4A), 3.32 (s, 3H,
=
4.14. Trichloroacetimidate (2-O-acetyl-3,4-di-O-benzyl-
J
a-
-glucopyranosyl)-(1“4)]-2-O-benzoyl-a/b-
pyranosyl, 6
L
-rhamnopyranosyl)-(1“3)-[(2,3,4,6-tetra-O-benzyl-a-
OCH3), 3.30–3.20 (m, 2H, H-4C, 5D), 2.14, 1.91 (2s,
6H, C(O)CH3), 1.47, 1.38 (2s, 6H, C(CH3)2), 1.35 (d,
3H, J5,6=6.2 Hz, H-6A), 1.30 (d, 3H, J5,6=6.2 Hz,
H-6B), and 0.95 (d, 3H, J5,6=6.2 Hz, H-6C); 13C
NMR: l 171.2, 170.1, 165.6 (3C, C(O)), 138.8–127.3
D
L
-rhamno-
Trichloroacetonitrile (1.2 mL, 11.96 mmol) and DBU
(24 mL, 160 mmol) were added to a solution of hemi-
acetal 26 (368 mg, 318 mmol) in CH2Cl2 (2 mL) and
the mixture was stirred at rt for 4 h. The reaction
mixture was concentrated and the residue was
purified by flash-column chromatography (solvent B,
4:1 containing 1‰ Et3N) to give 6 as a white foam
(Ph), 102.7 (C-1D, JC,H=161 Hz), 100.1 (C-1A, JC,H
=
171 Hz), 99.5 (C(CH3)2), 99.2 (C-1C, JC,H=168 Hz),
98.0 (C-1E, JC,H=169 Hz), 97.9 (C-1B, JC,H=169 Hz),
81.8 (C-3E), 81.4 (C-2E), 80.9 (C-4A), 79.9 (C-4C), 79.7
(C-3A), 79.6 (bs, C-3B), 78.8 (bs, C-4B*), 78.5 (bs, C-
3C*), 77.8 (C-4E*), 77.5 (C-2A), 77.3 (C-3D*), 75.5, 75.4,
75.0, 74.9, 73.9, 73.0, 72.9 (7C, OCH2), 72.5 (C-4D),
72.3 (C-2B), 71.6 (C-5E), 70.5 (OCH2), 68.6 (3C, C-2C,
5C, 6E), 67.7 (2C, C-5A, 5D), 67.3 (C-5B), 62.2 (C-6D),
57.3 (C-2D), 54.5 (OCH3), 29.2 (C(CH3)2), 23.5, 21.3
(2C, C(O)CH3), 19.3 (C(CH3)2), 18.5 (C-6B), 17.9 (C-
6A), and 17.7 (C-6C). ESMS for C101H115NO25 (M,
1741.78) m/z 1742.9 [M+H]+. Anal. calcd for
1
(343 mg, 83%); H NMR: l 8.73 (s, 1H, NH), 8.07–
7.13 (m, 35H, Ph), 6.35 (d, 1H, J1,2=2.8 Hz, H-1C),
5.68 (bs, 1H, H-2B), 5.58 (dd, 1H, J2,3=3.0 Hz, H-
2C), 5.06 (d, 1H, J1,2=3.3 Hz, H-1E), 5.04 (bs, 1H,
H-1B), 4.94 (d, 1H, J=11 Hz, OCH2), 4.82 (m, 3H,
OCH2), 4.66–4.34 (m, 8H, OCH2), 4.25 (bs, 1H, H-
3C), 4.06–3.97 (m, 3H, H-3E, 5C, 5E), 3.83–3.72 (m,
5H, H-6aE, 6bE, 4C, 4E, 3B), 3.67 (dq, 1H, J4,5=9.5
Hz, H-5B), 3.53 (dd, 1H, J2,3=9.7 Hz, H-2E), 3.32
(pt, 1H, J3,4=9.4 Hz, H-4B), 2.13 (s, 3H, C(O)CH3),
C101H115NO25: C, 69.60; H, 6.65; N, 0.89. Found: C,
69.40; H, 6.68; N, 0.83%.

F. Segat-Dioury, L. A. Mulard / Tetrahedron: Asymmetry 13 (2002) 2211–2222
2221
4.16. Methyl (3,4-di-O-benzyl-a-
(1“3)-[(2,3,4,6-tetra-O-benzyl-a-
(1“4)]-a- -rhamnopyranosyl-(1“3)-(2-acetamido-2-
deoxy-4,6-O-isopropylidene-b- -glucopyranosyl)-(1“2)-
3,4-di-O-benzyl-a- -rhamnopyranoside, 28
L
-rhamnopyranosyl)-
was purified by column chromatography (solvent D,
49:1) to give 29 (119 mg, 82%) as a white foam; [h]D
D
-glucopyranosyl)-
1
L
+22 (c 1.0); H NMR: l 7.37–7.26 (m, 40H, Ph), 5.70
D
(d, 1H, JNH,2=7.2 Hz, NH), 5.01 (d, 1H, J1,2=7.2
Hz, H-1D), 4.96–4.58 (m, 18H, H-1E, 1A, 1B, 1C, 14
OCH2), 4.46 (m, 2H, OCH2), 4.16 (bs, 1H, H-2C),
3.98–3.85 (m, 9H, H-3E, 5A, 5E, 3A, 2A, 5C, 3B, 2B,
6aD), 3.77–3.58 (m, 7H, H-6bD, 3C, 6aE, 6bE, 5B, 2D,
4E), 3.53–3.42 (m, 6H, H-2E, 4A, 4C, 3D, 5D, 4B), 3.36
L
Methanolic MeONa (1 M) was added to a solution
of 27 (150 mg, 86 mmol) in MeOH (3 mL) until the
pH reached 10, and the mixture was stirred at 60°C
overnight. TLC (solvent C, 5:1) showed the presence
of a more polar product. The mixture was neutralized
by addition of Amberlite IR 120 (H+), filtered, and
volatiles were evaporated. The crude residue was
purified by column chromatography (solvent C, 9:1)
to give the diol 28 (124 mg, 90%) as a white foam;
(pt, 1H,
J3,4=J4,5=9.3 Hz, H-4D), 3.33 (s, 3H,
OCH3), 2.98 (bs, 1H, OH-2C), 2.69 (bs, 1H, OH-2B),
2.69, 1.84 (2bs, 2H, OH-6D, OH-4D), 1.72 (s, 3H,
C(O)CH3), and 1.38–1.30 (m, 9H, H-6A, 6B, 6C); 13C
NMR: l 170.9 (C(O)), 138.7–128.0 (Ph), 102.3 (C-1D),
101.2 (C-1*B), 100.8 (C-1C), 100.0 (C-1*A), 98.4 (C-1E),
86.4 (C-3D), 81.5 (C-3E), 81.0 (C-4B*), 80.6 (C-2E*), 80.0
(C-3B*), 79.8 (C-4C*), 79.2 (2C, C-3A*, 3C), 79.1 (C-4*A),
77.6 (C-4E), 77.4 (C-2A), 75.7 (OCH2), 75.5 (C-4D),
75.4, 75.0, 74.9, 73.6, 73.2, 72.9, (7C, OCH2), 71.3
(C-5E), 70.5 (C-5D), 70.0 (C-2B), 69.1 (C-5A*), 68.6 (C-
5C), 68.4 (C-2C), 68.3 (C-6E), 67.6 (C-5*B), 62.9 (C-6D),
55.4 (C-2D), 54.6 (OCH3), 23.4 (C(O)CH3), and 18.4,
17.9, 17.8 (3C, C-6B, 6A, 6C). FABMS for
C89H105NO23 (M, 1555.71) m/z 1578.8 [M+Na]+.
Anal. calcd for C89H105NO23: C, 68.66; H, 6.80; N,
0.90. Found: C, 68.64; H, 6.89; N, 0.81%.
1
[h]D +21 (c 1.0); H NMR: l 7.39–7.25 (m, 40H, Ph),
5.44 (d, 1H, JNH,2=8.0 Hz, NH), 5.07 (d, 1H, J1,2
=
2.2 Hz, H-1C), 5.04 (d, 1H, J1,2=3.0 Hz, H-1E), 4.94
(d, 1H, J=10.8 Hz, OCH2), 4.86–4.44 (m, 15H,
OCH2), 4.68 (m, 2H, H-1A, 1B), 4.48 (d, partially
overlapped, 1H, H-1D), 4.20 (bs, 1H, H-2C), 4.06 (dq,
1H, J4,5=9.4, J5,6=6.2 Hz, H-5B), 3.89–3.69 (m, 13H,
H-5E, 3E, 2A, 3A, 3B, 6aD, 6bD, 2B, 5C, 2D, 3C, 6aE,
6bE), 3.66–3.58 (m, 4H, H-5A, 4E, 4D, 3D), 3.53–3.46
(m, 3H, H-2E, 4C, 4B), 3.35 (pt, 1H, J2,3=J3,4=9.3
Hz, H-4A), 3.32 (s, 3H, OCH3), 3.23 (m, 1H, H-5D),
3.13 (bs, 1H, OH), 2.35 (bs, 1H, OH), 1.66 (s, 3H,
C(O)CH3), 1.46 (s, 3H, C(CH3)2), 1.39–1.36 (m, 6H,
C(CH3)2, H-6C), and 1.32 (m, 6H, H-6A, 6B); 13C
NMR: l 170.1 (C(O)), 138.6–127.6 (Ph), 103.4 (C-1D),
101.4 (C-1C), 100.0, 99.8 (C-1A, 1B), 99.5 (C(CH3)2),
98.1 (C-1E), 81.4 (C-3E), 81.1, 81.0 (C-2E, 4*A), 80.4,
79.9 (C-3B, 3A), 79.8, 79.5 (C-4B*, 4C), 79.1 (C-3C),
77.8, 77.7, 77.6 (C-4E, 2A, 3D), 75.5, 75.4, 75.0, 74.8,
73.5, 73.4, 73.1 (7C, OCH2), 72.2 (C-4D), 72.0
(OCH2), 71.2 (C-5E), 70.7 (C-2B), 69.2 (C-5C), 68.4
(C-2C), 68.3 (C-6E), 67.8 (C-5D), 67.6 (C-5A), 66.9 (C-
5B), 62.2 (C-6D), 56.5 (C-2D), 54.5 (OCH3), 29.1
(C(CH3)2), 23.2 (C(O)CH3), 19.2 (C(CH3)2), 18.3 (C-
6C), 17.8 and 17.7 (2C, C-6B, 6A). FABMS for
C92H109NO23 (M, 1595.74) m/z 1618.8 [M+Na]+.
Anal. calcd for C92H109NO23: C, 69.20; H, 6.88; N,
0.88. Found: C, 69.09; H, 7.04; N, 0.96%.
4.18. Methyl a-
ranosyl-(1“4)]-a-
amido-2-deoxy-b-
rhamnopyranoside, 2
L
-rhamnopyranosyl-(1“3)-[a-
-rhamnopyranosyl-(1“3)-(2-acet-
-glucopyranosyl)-(1“2)-a-
D-glucopy-
L
D
L-
A solution of tetraol 29 (310 mg, 199 mmol) in a
mixture of MeOH (9 mL) and AcOH (1 mL) was
treated with 10% Pd–C catalyst (200 mg) as described
for the preparation of 1. Reverse phase chromatogra-
phy (solvent F, gradient), followed by lyophilization,
gave the targeted pentasaccharide 2 as a lyophilized
powder (126 mg, 76%); [h]D −12 (c 1.0, water); 1H
NMR: (D2O); l 5.10 (d, 1H, J1,2=3.6 Hz, H-1E),
4.90 (bs, 1H, H-1B), 4.76 (bs, 1H, H-1A), 4.75 (bs,
1H, H-1C), 4.65 (d, 1H, J1,2=8.5 Hz, H-1D), 4.08 (dq,
1H, J4,5=9.0 Hz, H-5C), 4.03 (m, 1H, H-2B), 3.99 (m,
1H, H-2A), 3.96–3.65 (m, 12H, H-3C, 2C, 6aD, 6aE,
6bE, 5E, 2D, 5B, 3A, 3B, 4C, 6bD), 3.60–3.33 (m, 8H,
H-3E, 5A, 3D, 4D, 2E, 5D, 4E, 4B), 3.31 (s, 3H, OCH3),
3.13 (pt, 1H, J3,4=J4,5=9.6 Hz, H-4A), 1.99 (s, 3H,
C(O)CH3), 1.27 (d, 3H, J5,6=6.2 Hz, H-6A), 1.21 (d,
3H, J5,6=6.0 Hz, H-6C), and 1.20 (d, 3H, J5,6=6.1
Hz, H-6B); 13C NMR: (D2O); l 175.1 (C(O)), 103.7
(C-1D, JC,H=161 Hz), 102.9 (C-1A, JC,H=171 Hz),
101.8 (C-1C, JC,H=168 Hz), 100.5 (C-1E, JC,H=169
Hz), 99.0 (C-1B, JC,H=169 Hz), 82.2 (C-3D), 79.4 (C-
3C), 79.2 (C-2A), 77.0 (bs, C-4C), 76.6 (C-4E), 73.3
(C-3E), 73.0 (C-4A), 72.7 (2C, C-4B, 5*E), 72.2 (C-2E),
71.5 (C-2C), 70.9 (2C, C-3A*, 2B), 70.0 (C-3B*), 70.1
(C-5D*), 70.0 (C-5B), 69.6 (C-5C), 69.3 (C-5A), 69.1 (C-
4D*), 61.4 (C-6D), 61.2 (C-6E), 56.3 (C-2D), 55.5
(OCH3), 23.1 (C(O)CH3), 18.4 (C-6C), and 17.4, 17.3
(2C, C-6A, 6B). High-resolution ESMS for
C33H57NO23 (M−H, 834.32431) m/z 834.32135 [M+
Na]+.
4.17. Methyl (3,4-di-O-benzyl-a-
(1“3)-[(2,3,4,6-tetra-O-benzyl-a-
(1“4)]-a- -rhamnopyranosyl-(1“3)-(2-acetamido-2-
deoxy-b- -glucopyranosyl)-(1“2)-3,4-di-O-benzyl-a-
rhamnopyranoside, 29
L
-rhamnopyranosyl)-
D
-glucopyranosyl)-
L
D
L-
50% aq. TFA (1 mL) was added to a solution of the
fully protected 27 (162 mg, 93 mmol) in CH2Cl2 (3
mL) and the mixture was stirred at 0°C for 50 min.
TLC (solvent C, 6:1) showed that the complete disap-
pearance of the starting material. Toluene was added
and volatiles were evaporated. The crude mixture was
solubilized in MeOH (3 mL), 1N methanolic MeONa
was added dropwise until the pH was 10, and the
mixture was stirred overnight at 60°C. TLC (solvent
C, 9:1) showed that the material had been trans-
formed into a more polar product. Neutralization
with Amberlite IR 120 (H+), filtration and evapora-
tion of the volatiles resulted in a crude product which

2222
F. Segat-Dioury, L. A. Mulard / Tetrahedron: Asymmetry 13 (2002) 2211–2222
14. Hanna, H. R.; Bundle, D. R. Can. J. Chem. 1993, 71,
Acknowledgements
125–134.
15. Mulard, L. A.; Cle´ment, M.-J.; Segat-Dioury, F.;
Delepierre, M. Tetrahedron 2002, 58, 2593–2604.
16. Bundle, D. R. In Topics in Current Chemistry; Carbohy-
drate Chemistry; Thiem, J., Ed.; Springer-Verlag: Berlin,
1990; Vol. 154, pp. 1–37.
The authors thank the C.A.N.A.M. for the scolarship
provided to F. Segat-Dioury. The authors are grateful
to J. Ughetto-Monfrin (Unite´ de Chimie Organique,
Institut Pasteur) for recording all the NMR spectra.
17. Pinto, B. M.; Reimer, K. B.; Morissette, D. G.; Bundle,
D. R. Carbohydr. Res. 1990, 196, 156–166.
18. Schmidt, R. R.; Kinzy, W. Adv. Carbohydr. Chem.
Biochem. 1994, 50, 21–123.
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